Conservationists have said wildlife could be “disappearing in the dark” after figures showed that three-quarters of England’s most precious habitats, wildlife and natural features have had no recent assessment of their condition.

The warning follows the publication of figures covering assessments of protected natural sites known as sites of special scientific interest (SSSIs) in the last five years. SSSIs are legally protected because they contain special features such as threatened habitats or rare species, and together they cover more than 1.1m hectares (2.7m acres), about 8% of England’s land area.

Nearly two-fifths of the habitats and other features for which SSSIs are protected were in an unfavourable condition, according to figures from the conservation agency Natural England.

They also show that only 3,384 – or about 25% – of features had been assessed for their condition since the start of 2019 up to last month. It leaves 10,148, or 75%, without an up-to-date assessment of how they are faring.

The figures, revealed after a request from PA Media, were described by conservationists as a reminder of the under-resourced state of environmental watchdogs.

SSSIs are integral to Britain’s international commitment to protect 30% of its land and seas for nature by 2030, a pledge made by Boris Johnson as prime minister and sometimes called the 30×30 commitment.

Richard Benwell, the chief executive of Wildlife and Countryside Link, said: “The protected site network is critical natural infrastructure supporting wildlife, health and wellbeing, and a resilient economy. But with over three-quarters of sites not inspected in the last five years, regulators will have no idea whether they are in good condition and the government won’t know where it should be targeting its efforts in order to reach critical 2030 targets.

“Wildlife could be disappearing in the dark while ecosystems break down. It’s like shutting the door on a new power plant and not visiting for a decade.”

More than 5,000 SSSI features, about 39% of the total, were in an unfavourable state in their last assessment, which could have been well before 2019. Of those, 10% were declining and 22% recovering.

About 40% of features were in a favourable condition, more than a fifth were classed as “not recorded” due to incomplete data, and less than 0.5% had been destroyed.

A spokesperson for the Department for Environment, Food and Rural Affairs said: “Protected sites are at the heart of our vision for making space for rare habitats and threatened species to thrive as well as green spaces for us all to enjoy. It’s why this government has wasted no time in establishing a rapid review of our plan to deliver on our legally binding targets for the environment, including measures to improve the condition of protected sites. We will deliver a new statutory plan that will help restore our natural environment.”

Natural England is developing a long-term programme to determine when SSSIs need to be assessed, as well as improving monitoring with remote sensing technology and greater use of data.

The amount of land that is “effectively protected” for nature in England has declined to just 2.93%, despite government promises to conserve 30% of it by 2030, according to research published in October.

The land figure was found to have been falling owing to declines in quality of SSSIs, which are changing because of the climate crisis, water pollution and overgrazing.